This invention relates generally to hydraulic fracturing and, more particularly, to downhole tools and methods used in the sliding sleeve method of hydraulic fracturing.
Hydraulic fracturing creates fractures in a reservoir rock formation in order to release oil and natural gas products from that formation. The two most common methods of creating the fractures are the “plug” method (or “plug-and-perf” method) and the “sliding sleeve” method.
One of the challenges with the sliding sleeve method is the occasional failure of the ball to reach or seat properly in the sliding sleeve of the next flow port or zone and, therefore, not open that fracture zone. The operator in the fracking rig often cannot tell if the flow port is open because formation characteristics vary along the wellbore, thereby making pressure readings difficult, if not impossible, to interpret. Therefore, the operator has no consistent indication that the fracture zone is actually open. Electronic sensors can be run along with the flow ports, but this is expensive and takes more time to install with more risk in deployment.
The lack of a clear indication that the zone is open does not happen on all port opening events, but does occur on some events throughout the process of fracturing along the length of the entire wellbore. This lack of opening indication can result in the hydraulic fracturing process being shut down to investigate if the next fracture zone of interest is actually opened. In cases in which the ball did not reach the next flow port, it is possible for one zone to be completely skipped in the fracturing process. If the zone is not open and fracture fluid continues to pump, then the zone prior to the zone of interest will receive additional fracture fluid. This additional fracture fluid could cause formation damage, reach into unwanted saltwater zones, and impede well production. In some cases, this can cause significant monetary losses.
Therefore, there is a need to improve the reliability of the sliding sleeve method so that an operator knows, with a high degree of certainty, that the ball has reached the fracture zone of interest and has opened up that zone.